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Introduction Of Exotic Fish & Its Impact On

Biodiversity

Puspendu SamantaFs-15/09

B.F.Sc 3rd Year 2nd Sem

A Seminar on -

AEM -328

Submitted by-

Introduction• Exotic fish species have been receiving international

attention in different forums including the important ones like Convention on Biological Diversity and also in the FAO Code of Conduct for Responsible Fisheries.

• While much of the recent attention has been mainly focused on the adverse impacts of alien fish introduction.

• There is realization that all alien species perform bad under every circumstances.

Why are they introduced?

• Exotic species of the fishes were introduced in many parts of the world with high hopes of promoting……..

1. Improving local fishery potential and for broadening species diversity in aquaculture programmes,

2. Sport fishing,

3. For aquarium keeping,

4. Improving aquaculture or open water fishery productivity,

5. Controlling of unwanted organisms (mosquitoes).

Exotic fishes transplanted in

INDIA

Species Home Year Purpose

1.Brown Trout (Salmo trutta fario)

U.K. 1863- 1900 For planting streams, lakes and reservoirs.

2. Loch Leven Trout (Salmo levensis)

U.K. 1863 For planting streams, lakes and reservoirs.

3. Rainbow Trout (Salmo gairdneri)

Sri Lanka & Germany

1907 For planting streams, lakes and reservoirs.

4. Eastern Brook Trout (Salvelinus fontinalis)

U.K. 1911 For planting streams, lakes and reservoirs.

5. Sockeye Salmon (Oncorhynchus nerka)

Japan 1968 For planting streams, lakes and reservoirs.

6. Atlantic Salmon (Salmo salar)

U.S.A. 1968 For planting streams, lakes and reservoirs.

Game Fishes :-

Species Home Year Purpose

1) Golden Carp (Carassius carassius)

U.K. 1870 Experimental culture

2) Tench (Tinca tinca)

U.K. 1870 Experimental culture

3) Gourami (Osphronemus goramy)

Java & Mauritius

1916 Experimental culture

4) Common Carp (Cyprinus carpio) [German Strain]

Sri Lanka 1939 Experimental culture

5) Tilapia (Oreochromis

mossambicus)

Africa 1952 Experimental culture

Food Fishes :-

Species Home Year Purpose

6) Common Carp (Cyprinus carpio) [Bangkok strain]

Thailand 1957 Experimental culture

7) Grass Carp (Ctenopahryngodon idella)

Japan 1957 Experimental culture and weed control

8) Silver Carp (Hypophthalmichthys molitrix)

Hong Kong

1959 Experimental culture

9) Tawes (Puntius javanicus)

Indonesia 1972 Experimental culture

Species Home Year Purpose

1) Guppy (Poecilia reticulata)

South America

1908 Mosquito control.

2) Top Minnow (Gambusia affinis)

Italy 1928 Mosquito control.

Species Home Purpose

1) Live bearers (27 species)

From various countries Aquarium keeping

2) Egg layers ( 261 speceis) 

From various countries Aquarium keeping

Larvicidal Fishes :-

Ornamental Fishes :-

Impact On Bio-diversity

• Exotic or alien fishes make some bad impact on aquatic biodiversity. Those impacts may be categorized as :

1) Genetic Impact,2) Ecological(including biological) Impact &3) Socio-economical Impact.

Genetic Impact

• The genetic impact of introduction of exotic fishes on native fishes can be classified into 2 categories :-

A. Reduction of effective population size by the ecological, biological & genetic effect of introduction. &

B. Alteration/extinction of gene pools of the species/stocks by crossbreeding or hybridization & backcrossing.

Introgression Through Hybridization

One of the reasons for the increased frequency of hybridization is introduction of exotic species.

Hybridization may lead to hybrid vigor or heterosis due to over dominance and heterozygocity at many loci or may lead to genetic pollution.

Thus, the result of hybridization in general and with exotic species in particular is unpredictable in advance.

Hybridization between an alien species and a native one leads to genetic introgression. This is the transmission of genes from one species to another through hybridization.

Extinction Due To Hybridization

Hybridization between exotic and native species has not only brought in genetic contamination but even resulted in species extinction in some cases.

Apache trout (Oncorhynchus apache) & Gila trout (O. gilae), two native species of Southwest USA, have faced extinction primarily due to hybridization with the introduced species, Cutthroat trout (O. clarkii) & O. mykiss.

Loss Of Traits

Loss of traits leading to economic value decline takes place in uncontrolled hybridization between exotic and native species.

Hybridization between Bighead (Aristichthys nobilis) & Silver carp (Hypophthalmichthys molitrix) showed beneficial properties in terms of growth, food conversion & disease resistance.

But in further uncontrolled hybridization of these fishes in later generation, the offspring lost the acquired beneficial traits.

Genetic Bottleneck

A genetic bottleneck is the sudden and drastic decline in numbers. It effectively samples (although not necessarily randomly) a few individuals from a larger gene pool, resulting in a remnant population with less overall variation.

Loss of variation has two components like reduction in variance of qualitative traits and loss of specific and usually rare alleles.

Inbreeding Depression

It is probably the most serious and yet most nebulous problem in small populations of endangered fishes.

It is mating of individuals related by common ancestry that share common genes due to descent than individuals randomly selected from the population.

Fitness characters with low heritability are generally effected in consanguuious matings including severe body deformity, growth reduction, behavioral changes and reproductive failures.

Ecological impacts

Competition of exotic fishes with the native species for living space with same niche preference, for food with fishes of similar types of feeding habits, or of omnivorous feeding habits ,or predation on native fishes by these, spreading parasites and pathogens, thereby are some common ecological concerns.

Predator-prey Interactions :-

Top carnivores are often viewed the most significant threat as introduced fishes.

Although the generality of this statement is not borne out by an analysis of the records in the Database on Introductions of Aquatic Species (DIAS).

Predation directly reduces population size of the prey species, and may cause cascading ecological effects, such as increased plant growth when herbivores are removed by top predators.

Competition can occur between alien and resident species for food, habitat, mates, or other essential resources.

Tilapia (Oreochromis spp.) and especially the Mozambique tilapia, Oreochromis mossabicus, are considered to be a threat to native diversity in many areas where they have been introduced and most of the impacts have been reported for inland waters.

O. mossambicus in the Philippines and Pacific islands competes for algae and other resources and has displaced preferred species of mullet, Mugil cephalus, brackishwater shrimp, Penaeus merguiensis, and milk fish, Chanos chanos in brackish water fish ponds.

competition:-

The spread of pathogens along with species transported or traded in aquaculture is a serious concern that is being dealt with by several international agencies such as FAO, World Health Organization (WHO), World Trade Organization (WTO) and the International Office of Epizootics (OIE).

Of particular concern to exotic species is that the level of uncertainty will be higher with new introductions on what pathogens may be present and may cause problems in the new environment.

For example, along with abalone that the California aquaculture industry imported from South Africa came a sabellid worm parasite that caused no problems in South Africa but has had devastating effects of abalone under culture in California; the impact on other Californian mollusks is unknown.

Disease Impact:-

Many species of freshwater animals greatly modify aquatic habitats when placed into a new area, e.g. beavers, crayfish, common carp, and grass carp.

The Asian clam, Corbicula fluminea, was probably introduced into the USA by Chinese immigrants as a food item (though possibly not for intentional farming) in 1938.

The clam has since spread widely to inland and coastal areas of 38 states in the USA. The most significant affect is in biofouling of freshwater systems, but the clam can grow in such large numbers as to alter the flow and substrate in streams and lakes and can remove large amounts of phytoplankton from the water column.

Habitat Impacts:-

Socio-economic impacts

• The economic impacts can be seen at two levels - 1. capture fisheries and 2. aquaculture. • Since the exotic fishes never fetch higher price than the native

varieties and also the decline of native fish production is observed in the presence of exotic species in natural waters , the total economic returns declined for the stakeholders of the capture fisheries.

• In aquaculture however it provided immediate gain, in most cases without consideration of the long term ecological consequences.

Conclusion

• The global experience and the present status of introduction of exotic species in different counties including India their ecological, biological and genetic impact analysis in this contribution indicates their generally deleterious effect on autochthonous species.

• In addition to direct devastating eco-biological impacts, it has also been seen that some fish are even extinct owing to loss of genetic variability and heterozygosity.

Reference• Consequence Of Alien Fish Introduction – - by P. Das.(In Fishing Chimes, Vol 26 No. 10,January

2007).• Plecostomus multiradiatus an armored catfish from

freshwater ponds near Kunnamkulam, Kerala and its possible impact on indigenous fishes – by Ajithkumar, C.R., C.R. Biju and R. Thomas (1998). LAK News, Limnological Association of Kerala, 1-2.

• Fish fauna of Bharathapuzha (Nila river), Kerala. J. Bombay nat. Hist. Soc – by Bijukumar, A. and S. Sushama (In press).